1. Field of the Invention
The present invention relates to a high-precision instantaneously generated torque detection device for a three-phase motor. The three-phase motors include three-phase motors such as a three-phase induction motor, a three-phase synchronous motor, a three-phase synchronous induction motor, a brushless DC motor, an AC servo motor, a PM type motor, a three-phase reluctance motor, a permanent magnet type synchronous motor, a surface permanent magnet synchronous motor (SPM motor), an interior permanent magnet synchronous motor (IPM motor), a permanent magnet type induction motor, and a permanent magnet type synchronous induction motor.
2. Description of the Related Art
An instantaneously generated torque measurement device for a three-phase induction motor described in Japanese Examined Patent Publications No. 2591901 and No. 2619168 which are known at present, a torque is calculated from an applied voltage and a current. However, since not only a current which is contributed to a torque but also a current including a no-load current which is not contributed to a torque are detected in current detection, the torque is not precisely calculated.
According to the present invention, there is provided a detection device having the following configuration. Before an instantaneously generated torque is calculated from the instantaneous values of an applied voltage and a current of a three-phase motor, a no-load current which is not contributed to the torque is detected in advance, the instantaneous value of the no-load current is subtracted from an instantaneous current detected from the three-phase motor in a drive state to calculate a high-precision instantaneously generated torque, or a no-load current which is not contributed to the torque is detected in advance before the instantaneously generated torque is calculated from the instantaneous values of the applied voltage and the current of the three-phase motor, an instantaneous no-load loss torque corresponding to the no-load current is calculated, the no-load loss torque is subtracted from the value of the instantaneously generated torque calculated from the instantaneous values of the applied voltage and the current of the three-phase motor in the drive state, so that a high-precision instantaneously generated torque and an average generated torque of the three-phase motor can be detected.
A device according to the present invention comprises a calculator for detecting a no-load current which is not contributed to a torque in advance before an instantaneously generated torque is calculated from instantaneous values of an applied voltage and a current of a three-phase motor, subtracting an instantaneous value of the no-load current from an instantaneous current detected from the three-phase motor in a drive state, and calculating a high-precision instantaneously generated torque, or a calculator for detecting a no-load current which is not contributed to a torque in advance before an instantaneously generated torque is calculated from instantaneous values of an applied voltage and a current of a three-phase motor, calculating an instantaneous no-load loss torque corresponding to the no-load current, subtracting the no-load loss torque from the value of the instantaneously generated torque calculated from instantaneous values of the applied voltage and the current detected from the three-phase motor in a drive state, and calculating a high-precision instantaneously generated torque.
In the present invention, before an instantaneously generated torque is calculated from the instantaneous values of the applied voltage and the current of the three-phase motor, an instantaneous current in a no-load state is stored in advance, or calculation and storage of an instantaneous loss torque in a no-load state are performed. Calculation and storage of an average torque related to time are performed on the basis of the instantaneous loss torque in the no-load state, the stored no-load current or the instantaneous loss torque in the no-load state are considered when the instantaneously generated torque is calculated from the voltage and the current of the three-phase motor in a drive state, so that a high-precision instantaneously generated torque can be detected. A high-precision average torque can also be detected in consideration of the average torque in the no-load state.